Electro-Hydraulic Rivet and Method of Riveting and Welding Parts

ABSTRACT

A method of riveting two metal parts through a hole with an electro-hydraulic riveting tool. The electro-hydraulic riveting tool includes a tube that is inserted in the hole and an electrode that is inserted within the tube. A liquid is contained within the tube and the electrode is immersed in the liquid. A stored charge is discharged through the electrode to create a shockwave within the fluid that forms the tube into a rivet structure and creates solid state weld between the rivet flanges and the parts that are joined.

TECHNICAL FIELD

This disclosure relates to a method of joining metal parts with a rivetthat welds to the parts in an electro-hydraulic forming process.

BACKGROUND

Manufacturers face problems relating to joining aluminum parts and othertypes of parts. For example, aluminum alloys are characterized by havingless stiffness due to a lower modulus of elasticity. Aluminum is alsodifficult to spot, or resistance, weld because increased current isrequired and inconsistent results are obtained.

Aluminum parts are frequently joined by being riveted together.Self-piercing rivets formed of steel may be used, but the dissimilarmetals may create a galvanic corrosion problem. Rivets are generallyweak and tend to be anisotropic in that they have different strengthcharacteristics in different directions.

In general, welds are stronger than rivets for connecting parts, such assheet metal parts together. Applicant's co-pending application entitled“Metal Members and Assemblies that have Reinforced Punch Holes andMethod of Forming the Holes”, U.S. Ser. No. 13/157,357 discloses amethod of punching holes and reinforcing holes in sheet metal members,but does not relate to joining panels together. Further, Applicant'sco-pending application does not disclose electro-hydraulically formingthe circular reinforcement ring about the hole.

The following references were considered before filing this application:U.S. Pat. Nos. 6,301,766; 3,673,833; 6,094,809; 5,521,782; and5,471,865.

SUMMARY

According to one aspect of the present invention, a method of rivetingtwo metal parts through a hole is disclosed. According to the method, anelectro-hydraulic riveting assembly is inserted into a hole in the part.The riveting assembly includes a tube, an electrode, and a liquidcontained within the tube. A stored charge is applied to the electrodeto create a shockwave within the liquid. The tube is formed by the shockwave to overlap two outer surfaces of the two parts around the hole.

In one embodiment of the method, first and second rings are assembledaround the tube and to each of the outer surfaces of the parts beforethe forming step. Alternatively, the method may comprise forming a holein each of the metal parts and also forming a rim flange around each ofthe holes that extends axially from the outer surface of each of theholes.

According to another aspect of the method, the electro-hydraulicriveting assembly may comprise end caps that are secured to first andsecond ends of the tube to seal the liquid within the tube. The end capsmay be plastic caps that are assembled to the tube. Theelectro-hydraulic riveting assembly may be a cartridge that ispreassembled before inserting into the hole in the parts. Alternatively,a plastic bag type of enclosure may be used to contain the liquid in theelectrode within the tube.

During the forming step, a pair of circular flanges may be formed fromopposite ends of the tube that are expanded radially outwardly tooverlap the outer surface of each of the two parts around the hole. Thecircular radial flanges may form a metallurgical bond to the outersurfaces of the two parts. The metallurgical bond may constitute a solidstate weld formed by impact.

According to another aspect of the method disclosed herein, a method ofjoining at least two metal parts is disclosed. The method may comprisethe steps of forming a first hole in a first metal part and a secondhole in a second metal part. The first and second parts are assembledtogether with the first and second holes in alignment. A tube isinserted into the first and second holes and a wire electrode isinserted into the tube. A liquid is contained between the wire electrodeand the tube. A stored charge is applied to the wire electrode to createa shockwave within the liquid. A pair of circular flanges is formed fromopposite ends of the tube that are expanded radially outwardly by theshockwave to overlap the outer surface of each of the two parts aroundthe hole.

According to another aspect of this disclosure, a rivet is disclosed forsecuring a pair of metal parts together that define a hole. The rivetcomprises a tubular member that extends through the hole from a firstside of the two parts to a second side of the two parts. The tubularmember has a first circular flange that engages the first side and asecond circular flange that engages the second side. A first solid stateweld is formed between the first flange and the first side and a secondsolid state weld is formed between the second flange and the secondside.

The above aspects of the method and apparatus will be better understoodin view of the attached drawings and the following detailed descriptionof the illustrated embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic cross-section view of two parts defining a holein which an electro-hydraulic riveting tool is inserted in the hole;

FIG. 2 is a diagrammatic cross-section view of a tube beingelectro-hydraulically formed into a rivet that is welded by impact tothe outer surfaces of the parts;

FIG. 3 is a diagrammatic cross-section view of an embodiment of theelectro-hydraulic forming and impact welding tool inserted in a holeformed by two sheets that also includes a ring around the hole thatcreates a pulsed welding angle;

FIG. 4 is a diagrammatic cross-section view of the rivet made inaccordance with the tool shown in FIG. 3 holding the parts together withflanges impact welded to the outer surfaces of the parts;

FIG. 5 is a diagrammatic cross-section view of another embodiment of theelectro-hydraulic riveting tool assembled within a hole defined by theparts that include a rim flange formed around each of the holes andextending axially from the outer surface of the parts;

FIG. 6 is a diagrammatic cross-section view of a rivet formed around thetwo panels shown in FIG. 5 with the circular flanges impact welded tothe outer surface of the panel;

FIG. 7 is an alternative view of an electro-hydraulic forming tool inwhich the liquid is retained within a bag-like plastic membrane; and

FIG. 8 is a photomicrograph showing the impact weld microstructure atthe pulse welding interface.

DETAILED DESCRIPTION

A detailed description of the illustrated embodiments of the presentinvention is provided below. The disclosed embodiments are examples ofthe invention that may be embodied in various and alternative forms. Thefigures are not necessarily to scale. Some features may be exaggeratedor minimized to show details of particular components. The specificstructural and functional details disclosed in this application are notto be interpreted as limiting, but merely as a representative basis forteaching one skilled in the art how to practice the invention.

Referring to FIG. 1, an electro-hydraulic riveting assembly, or tool, isgenerally indicated by reference numeral 10. The assembly 10 is receivedin a first part 12 that defines a first hole 14 and a second part 16that defines a second hole 18. The parts may be sheet metal parts or oneor both of the parts may be molded, cast, or otherwise formed. Part ofthe electro-hydraulic riveting assembly 10 is a tube 20 that ispreferably an aluminum tube if the first and second parts 12 are formedof aluminum. An electrode 24 is placed inside the tube 20 and a firstend cap 26 and second end cap 28 are attached to opposite ends of thetube 20 to contain a liquid 30 in which the electrode 24 is immersed.The electrode 24 is connected to a source of stored charge, such as abank of capacitors, as indicated by the plus and minus sign. Theelectrode 24 is a wire electrode that may be formed of aluminum wire.When the electrode 24 receives the stored charge, the electrodevaporizes creating a shockwave within the liquid 30 that deforms thetube 20 to join the two parts 12, 16 together in a local area.

Referring to FIG. 2, the tube 20 is shown being formed in response tothe discharge of the wire electrode 24. The tube generally indicated byreference numeral 20 includes a first flange 32 that is partially formedtoward the outer side of the first part 12. A second flange 34 is shownpartially formed toward the outer surface of the second part 16. Thetube 20 remains within the first and second holes 14, 18 during theforming process and thereafter. The first and second partially formedflanges 32, 34 form a first rivet flange 36 and a second rivet flange 38when they fully engage the first part 12 and second part 16,respectively. A first solid state weld 40 is formed between the firstrivet flange 36 and the first part 12 and a second solid state weld 42is formed between the second rivet flange 38 and second part 16. Thesolid state welds 40, 42 form a regular wave structure at a pulsedwelding interface that will be described subsequently with reference toFIG. 8. A solid state weld is formed without melting the rivet or thesheets. Consequently, there is no loss of tensile or shear strengthcaused by the formation of the weld. The weld forms a strong joint thatis superior in strength to conventional rivet joints.

Referring to FIG. 3, an alternative embodiment is shown in which a firstring 48 is assembled to one side of the first part 12 and about the tube20. A second ring 50 is assembled to the outer side of the second part16 and is also disposed about the tube 20. The first and second rings48, 50 are provided to increase the extent of the pulse wall. The rings48, 50 cause the first and second rivet flanges 36, 38 to increase theimpact angle of the tube 20 as it is formed into the rivet flanges 36,38. The impact angle is preferably approximately 7° relative to theouter surfaces of the first and second parts 12 and 16. The samereference numerals are used in FIGS. 3 and 4 as were used in FIGS. 1 and2. The electro-hydraulic riveting tool 10 is shown in FIG. 3 insertedwithin the first and second holes 14, 18 that are formed in the firstand second parts 12 and 16, respectively. The electrode 24 is immersedin a liquid 30 that is retained within the tube 20 by the end caps 26and 28.

Referring to FIG. 4, the first and second rivet flanges 36 are shownfully formed about the rings 48 and 50. First and second solid statewelds 40 and 42 are formed where the first and second rivet flanges 36and 38 impact against the outer surfaces of the first and second parts12 and 16, respectively. The tube 20 extends through the holes 14 and 18and secures the first part 12 and second part 16 together.

Referring to FIG. 5, an alternative embodiment is shown wherein a firstrim flange 52 is formed on a first part 54 that defines a first hole 56.A second rim flange 60 is provided on a second part 62 that defines asecond hole 64. An electro-hydraulic riveting cartridge 66 is showndisposed within the first and second holes 56 and 64. The rivetingcartridge 66 includes a rivet tube 68 that is disposed about a moldedcase 70. The molded case 70 is preferably a molded plastic enclosurethat is received within an aluminum rivet tube 68. An electrode 72 isdisposed within the molded case 70 and is immersed in a liquid 76. Theriveting cartridge 66 is discharged when it is connected to a source ofstored electrical charge that sends a shockwave through the liquid 76,as previously described with reference to FIGS. 1-4.

Referring to FIG. 6, the first and second parts 54 and 62 are shownjoined together by the rivet tube 68 after forming. A first rivet flange78 and a second rivet flange 80 are shown formed against the outersurface of the first part 54 and second part 62. The impact of theflanges is enhanced by providing the rim flanges 52 and 60 that createangles of approximately seven degrees during the impact of the rivetflanges into the part surfaces 54 and 62. The rim flanges enhance theformation of a first solid state weld 82 and a second solid state weld84 between the first and second rivet flanges 78 and 80 and the firstand second parts 54 and 62.

Referring to FIG. 7, an another alternative embodiment is shown in whicha plastic bag 88 is substituted for the electro-hydraulic rivetingassembly described with reference to FIG. 1. The same reference numeralsare used with reference to FIG. 7 as were used with reference to FIG. 1because all of the other parts are essentially unchanged. The plasticbag 88 is received within the tube 20. The tube 20 is inserted in thefirst and second holes 14 and 18 that are formed in the first and secondparts 12 and 16. An electrode 24 is disposed within the plastic bag 88and the plastic bag is filled with a fluid 30. The electrode isdischarged by connecting to a source of stored charge, as was previouslydescribed with reference to FIG. 1. When the electrode 24 is discharged,the tube is formed, as previously described with reference to FIGS. 1and 2. The several different embodiments of the EHF tool and the severaldifferent hole structures including a plain hole, a ring attachment or arim flange may be interchanged in any combination.

Referring to FIG. 8, a photomicrograph is shown of a first part 90 thatis welded in the solid state weld to a rivet flange. A pulsed weldinterface 94 is shown to comprise a regular wave structure at the pulsedwelding interface. There is no melting of the material of the first part90 or rivet flange 92. Since there is no melting of the materials, thereis no loss of tensile or shear strength. This results in a localizedjoining of the rivet to the part surface, as previously described withreference to FIGS. 1-7. The pulsed welding interface creates a strongjoint that is superior to the strength of a conventional riveted joint.

While exemplary embodiments are described above, it is not intended thatthese embodiments describe all possible forms of the invention. Rather,the words used in the specification are words of description rather thanlimitation, and it is understood that various changes may be madewithout departing from the spirit and scope of the invention.Additionally, the features of various implementing embodiments may becombined to form further embodiments of the invention.

What is claimed is:
 1. A method of riveting two metal parts that definea hole, comprising the steps of: inserting an electro-hydraulic rivetingassembly into the hole in the parts, the assembly including a tube, anelectrode, a liquid contained within the tube; and applying a storedcharge to the electrode to create a shock wave within the liquid; andforming the tube with the shock wave to overlap two outer surfaces ofthe two parts around the hole.
 2. The method of claim 1 furthercomprising: assembling a first ring and a second ring around the tubeand to each of the outer surfaces of the parts before the forming step.3. The method of claim 1 further comprising: forming the hole in each ofthe metal parts and forming a rim flange around each of the holes thatextends axially from the outer surface of each of the two parts.
 4. Themethod of claim 1 wherein the electro-hydraulic riveting assemblyfurther comprises a first end cap and a second end cap that are securedto a first end and a second end of the tube to seal the liquid withinthe tube.
 5. The method of claim 4 wherein the end caps are plastic capsthat are assembled to the tube.
 6. The method of claim 4 wherein theelectro-hydraulic riveting assembly includes a molded cartridge that ispreassembled to the tube before inserting in the hole in the parts. 7.The method of claim 1 further comprising a plastic bag that contains theliquid and the electrode within the tube.
 8. The method of claim 1wherein during the forming step a pair of circular flanges are formedfrom opposite ends of the tube that are expanded radially outwardly tooverlap the outer surface of each of the two parts around the hole. 9.The method of claim 8 wherein the pair of circular radial flanges form ametallurgical bond to the outer surfaces of the two parts.
 10. Themethod of claim 9 wherein the metallurgical bond is a solid state weld.11. The method of claim 9 further comprising: assembling a first ringand a second ring around the tube and to each of the outer surfaces ofthe parts before the forming step.
 12. The method of claim 9 furthercomprising: forming the hole in each of the metal parts and forming arim flange around each of the holes that extends axially from the outersurface of each of the two holes.
 13. A method of joining at least twometal parts, comprising the steps of: forming a first hole in a firstmetal part; forming a second hole in a second metal part; assembling thefirst and second parts together with the first and second holes inalignment; inserting a tube into the first and second holes; inserting awire electrode into the tube; containing a liquid between the wireelectrode and the tube; applying a stored charge to the wire electrodeto create a shock wave within the liquid; forming a pair of circularflanges from opposite ends of the tube that are expanded radiallyoutwardly by the shock wave to overlap the outer surface of each of thetwo parts around the hole.
 14. The method of claim 13 wherein the pairof circular radial flanges form a metallurgical bond to the outersurfaces of the two parts.
 15. The method of claim 14 wherein themetallurgical bond is a solid state weld.
 16. The method of claim 14further comprising: assembling a first ring and a second ring around thetube and to each of the outer surfaces of the parts before the formingstep.
 17. The method of claim 14 further comprising: forming a rimflange around each of the holes that extends axially from the outersurface of each of the two holes.
 18. A rivet for securing a pair ofmetal parts together that define a hole comprising: a tubular memberthat extends through the hole from a first side of the two parts to asecond side of the two parts, the tubular member having a first circularflange that engages the first side and a second circular flange thatengages the second side; and a first solid state weld formed between thefirst flange and the first side and a second solid state weld formedbetween the second flange and the second side.
 19. The rivet of claim 18further comprising a first ring and a second ring disposed around thetube with each ring being disposed adjacent one of the first and secondsides of the parts.
 20. The rivet of claim 18 further comprising a rimflange formed around the hole on the first side and the second side ofthe parts that extends axially outwardly from the outer surface of eachof the two parts.